1. Field of the Invention
The invention relates generally to the field of oil and gas well services. More specifically, the present invention relates to an apparatus that provides a pressure seal around a wireline during oil field service operations.
2. Description of Related Art
Numerous techniques, generally known as well logging, exist for collecting geological data from oil and/or gas wells, where the geological data is useful for locating potential hydrocarbon bearing reservoirs. Well logging is also used for estimating the capacity of the potential hydrocarbon bearing reservoirs. Many types of well logging practices exist. They include neutron logs, induction logs, and acoustic logs. In each of the aforementioned well logging techniques a well logging tool is deposited into the wellbore and travels through the well bore collecting geological data about the region surrounding the well bore. Generally the well logging tool produces a signal, either electrical, nuclear, or acoustical, which is directed into the area adjacent the well bore. The reflection or propagation of the emitted signal is then retrieved by the tool or by another piece of equipment suitably located. The retrieved signals are stored and analyzed in order to evaluate the potential for hydrocarbon production in the particular geological formation being analyzed, monitor reservoir performance, or to evaluate wellbore mechanical integrity.
Generally, the well logging tool is inserted into the well bore attached to a wireline. The tool is raised and lowered by the wireline, and data is transmitted through the wireline for introducing signals to the well logging tool from the surface. The wire line can also transmit data recovered from within the well bore to the surface for collection and analysis.
As a secondary safety measure, a pressure containment apparatus, or pack off head, is often installed on the well during wireline operations. Wireline (or slick-line) pack off heads (oil savers) have been used by the oil field service industry for many years. A pack off head is designed to make a pressure seal around a wireline to contain the well pressure during trips in and out of the well. If during wireline operations a well kick were experienced, an unsafe condition would occur if the well head was not contained but instead left open to atmosphere. A typical pack off head includes a hard rubber insert with a passage where the wire line passes through the annulus. To seal around the wireline, the hard rubber insert is axially compressed, which reduces the cross sectional area of the passage. Reducing the cross sectional area of the passage causes the inner radius of the passage to fit snugly around the outer radius of the wire line, thus preventing fluid flow through the passage. Although the passage snugly seals around the outer radius of the wire line, the wire line is still able to freely traverse through the passage.
Traditionally, pack off heads have been manual or hydraulic. A manual style pack off head is usually comprised of a threaded cap that compresses the rubber packing element as the cap is screwed down onto the head assembly. This operation is typically performed by hand. The hydraulic style pack off head has a hydraulic cylinder that is expanded via hydraulic pressure provided by a hand pump connected to the head by a hydraulic hose. The pack off head cylinder expands as pressure is supplied to it, expansion of the pack off head cylinder in turn compresses the pack off element. Both the manual and the hydraulic pack off heads compress a packing element to provide a seal around the wireline and both require personnel to perform this function.
Therefore, a method or an apparatus is desired that provides an automatic pressure sealing function around a wireline when the pack off head is located in an area that is not accessible to be either manually or hydraulically operated while a wireline is being lowered into and drawn from a hydrocarbon producing wellbore.
One embodiment of the present invention discloses a well pressure activated pack off head to be used in conjunction with a wellhead situated on a hydrocarbon producing wellbore. The well pressure activated pack off head comprises a hollow body formed for coaxial connection to the wellhead, the hollow body must also provide for unobstructed passage of a data transmitting wireline therethrough.
Disposed within the hollow body is a pack off rubber with a passage formed along its longitudinal axis for passage of a data transmitting wireline therethrough The pack off rubber is coaxially situated within the hollow body. The pack off rubber can be formed from numerous materials, but the material must be pliable enough under the conditions of use to provide a pressure seal between it and the wireline passing through its axis.
Also located in the hollow body, above and proximate to the pack off rubber, is a pack off bushing. The pack off bushing is coaxial to the hollow body and has an axial passage formed along its axis to allow for passage of a data transmitting wireline through its axis. The pack off bushing should have a higher hardness than the pack off rubber, typical materials include brass or hard face steel.
The well pressure activated pack off head further includes a piston coaxially situated within the hollow body and also has an axial passage formed concentric along its axis that allows for passage of a data transmitting wireline through it. The bottom of the piston is its wellbore pressure side and its top is its ambient pressure side. The wellbore pressure side of the piston is in pressure communication with the wellbore. The ambient pressure side of the piston is in pressure communication with the ambient space surrounding the pressure pack off head. The piston is situated below the pack off rubber, which puts the pack off rubber between the piston and the pack off bushing.
When the pressure of the wellbore, and thus the wellbore pressure side, exceeds the ambient pressure, the pressure differential experienced by the piston urges it toward the pack off bushing and pack off rubber. Continued upward movement of the piston causes the piston to contact the pack off rubber and push the pack off rubber against the pack off bushing. This pushing action compresses the pack off rubber between the piston and the pack off bushing such that compression of the pack off rubber compresses the pack off rubber axial passage around the data transmitting wireline. Compression of the pack off rubber axial passage around the data transmitting wireline eventually provides a pressure seal between the pack off rubber axial passage and the data transmitting wireline passing therethrough. The well pressure activated pack off head can also include a rubber compressor disposed between the piston and the pack off rubber, the rubber compressor transmits the axial compressing force from the piston to the pack off rubber.
To prevent pressure spikes in the wellbore from causing transient high forces upon the pack off rubber, the pressure pack off head includes a pressure regulator that controls the pressure between the wellbore and the piston. One example of a pressure regulator is a restriction orifice that regulates the pressure differential across the piston which limits the maximum force that the piston can apply to the pack off rubber (or the rubber compressor).
Also included in the well pressure activated pack off head is a spring that urges the piston away from said pack off rubber when the spring force exceeds the force experienced by the piston resulting from the pressure differential across its two sides. The size, configuration, and material of the spring is based on the application of the well pressure activated pack off head.
An alternative embodiment of the well pressure activated pack off head also includes a hollow body, a piston, a pack off rubber, and a pack off bushing axially situated in the hollow body. Here the piston has a wellbore pressure side and an ambient side. Also included in this alternative is a hydraulic piston and a means for communicating pressure from the ambient pressure side of the piston to the hydraulic piston.
Within the pressure communication means is a pressure regulator that controls the pressure that is delivered to the hydraulic piston from the ambient pressure side of the piston. As in the first embodiment, the pressure control means limits pressure excursions experienced in the wellbore from exerting high compression forces onto the pack off rubber.
Like the first embodiment, the alternative embodiment operates on the principal that the wellbore pressure will exceed the ambient pressure around the pack off head. The pressure differential is then utilized to produce a force that compresses the hydraulic piston against the pack off rubber, this squeezes the pack off rubber around the data transmitting wireling to providesa pressure seal around the pack off rubber and the data transmitting wireline. Also included in the alternative embodiment of the well pressure activated pack off head is a spring axially provided in the hollow body situated to urge the hydraulic piston away from the pack off rubber when the force experienced by the pressure differential across the hydraulic piston is lower than the spring force.
A third embodiment of a well pressure activated pack off head also comprises a hollow body, a pack off rubber, a pack off bushing, and a piston axially located in the hollow body. Like the other embodiments, these components are all formed to allow free passage of a wireline along their axis.
The piston has a top side, a bottom side, and a shaft connecting the piston top side to a rubber compressor. The piston bottom side is in pressure communication with the wellbore, and the pack off rubber is situated between said pack off bushing and said rubber compressor.
Like the other embodiments, this embodiment works on the principal of a force resulting from a pressure differential across an object. Because the wellbore pressure will generally exceed the ambient pressure around the well pressure activated pack off head, those two pressures are disposed across opposite faces of an object to produce a force, here the object is the piston. The resulting force across the piston is used to compress the pack off rubber against the pack off bushing. A compressed pack off rubber will result in a pressure seal between it and a data transmitting wireline passing through the axial passage of the pack off rubber.